Designation: E2126 – 11
Standard Test Methods for
Cyclic (Reversed) Load Test for Shear Resistance of Vertical Elements of the Lateral Force Resisting Systems for
Buildings
1This standard is issued under the fixed designation E2126; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 These test methods cover the evaluation of the shear stiffness, shear strength, and ductility of the vertical elements of lateral force resisting systems, including applicable shear connections and hold-down connections, under quasi-static cyclic (reversed) load conditions.
1.2 These test methods are intended for specimens con- structed from wood or metal framing braced with solid sheathing or other methods or structural insulated panels.
1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use.
2. Referenced Documents 2.1 ASTM Standards:2
D2395 Test Methods for Specific Gravity of Wood and Wood-Based Materials
D4442 Test Methods for Direct Moisture Content Measure- ment of Wood and Wood-Base Materials
D4444 Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters
E564 Practice for Static Load Test for Shear Resistance of Framed Walls for Buildings
E575 Practice for Reporting Data from Structural Tests of Building Constructions, Elements, Connections, and As- semblies
E631 Terminology of Building Constructions 2.2 ISO Standard:3
ISO 16670 Timber Structures—Joints Made with Mechani- cal Fasteners—Quasi-static Reversed-cyclic Test Method 2.3 Other Standards:4
ANSI/AF&PA NDS National Design Specification for Wood Construction
3. Terminology
3.1 For definitions of terms used in this standard, see Terminology E631.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 ductility ratio, cyclic (D),n—the ratio of the ultimate displacement (Du) and the yield displacement (Dyield) of a specimen observed in cyclic test.
3.2.2 elastic shear stiffness (Ke) (see9.1.4,Fig. 1),n—the resistance to deformation of a specimen in the elastic range before the first major event (FME) is achieved, which can be expressed as a slope measured by the ratio of the resisted shear load to the corresponding displacement.
3.2.3 envelope curve(seeFig. 2),n—the locus of extremi- ties of the load-displacement hysteresis loops, which contains the peak loads from the first cycle of each phase of the cyclic loading and neglects points on the hysteresis loops where the absolute value of the displacement at the peak load is less than that in the previous phase.
3.2.3.1 Discussion—Specimen displacement in the positive direction produces a positive envelope curve; the negative specimen displacement produces a negative envelope curve.
The positive direction is based on outward movement of the hydraulic actuator.
3.2.4 envelope curve, average (see Fig. 3), n—envelope curve obtained by averaging the absolute values of load and displacement of the corresponding positive and the negative envelope points for each cycle.
3.2.5 equivalent energy elastic-plastic (EEEP) curve (see 9.1.4,Fig. 1),n—an ideal elastic-plastic curve circumscribing
1These test methods are under the jurisdiction of ASTM CommitteeE06on Performance of Buildings and are the direct responsibility of SubcommitteeE06.11 on Horizontal and Vertical Structures/Structural Performance of Completed Struc- tures.
Current edition approved May 1, 2011. Published May 2011. Originally approved in 2001. Last previous edition approved in 2010 as E2126 – 10. DOI:
10.1520/E2126-11.
2For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [email protected]. ForAnnual Book of ASTM Standardsvolume information, refer to the standard’s Document Summary page on the ASTM website.
3Available from International Organization for Standardization (ISO), 1, ch. de la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://
www.iso.ch.
4Available from American Forest and Paper Association (AF&PA), 1111 19th St., NW, Suite 800, Washington, DC 20036, http://www.afandpa.org.
Copyright. (C) ASTM International, 100 Barr Harbor Drive, PO Box C-700 West Conshohocken, Pennsylvania 19428-2959, United States
an area equal to the area enclosed by the envelope curve between the origin, the ultimate displacement, and the dis- placement axis. For monotonic tests, the observed load- displacement curve is used to calculate the EEEP curve.
3.2.6 failure limit state,n—the point on the envelope curve corresponding to the last data point with the absolute load equal or greater than |0.8Ppeak|, as illustrated inFig. 1.
3.2.7 failure load (Pu), n—the load corresponding to the failure limit state.
3.2.8 first major event (FME),n—the first significant limit state to occur (see limit state).
3.2.9 limit state,n—an event that demarks the two behavior states, at which time some structural behavior of the specimen is altered significantly.
3.2.10 specimen,n—the vertical element of the lateral force resisting system to be tested. Example of specimens are walls, structural insulated panels, portal frames, etc. A specimen can be a single element or an entire line of resistance within a lateral force resisting system.
3.2.11 stabilized response, n—load resistance that differs not more than 5 % between two successive cycles at the same amplitude.
3.2.12 strength limit state (seeFig. 1),n—the point on the envelope curve corresponding to the maximum absolute dis- placementDpeakat the maximum absolute load (Ppeak) resisted by the specimen.
3.2.13 ultimate displacement, cyclic (Du),n—the displace- ment corresponding to the failure limit state in cyclic test.
3.2.14 ultimate displacement, monotonic (Dm), n—the dis- placement corresponding to the failure limit state in monotonic test.
3.2.15 yield limit state, n—the point in the load- displacement relationship where the elastic shear stiffness of the assembly decreases 5 % or more. For specimens with nonlinear ductile elastic response, the yield point (Dyield,Pyield) is permitted to be determined using the EEEP curve (see9.1.4).
4. Summary of Test Method
4.1 The elastic shear stiffness, shear strength and ductility of specimens are determined by subjecting a specimen to full- reversal cyclic racking shear loads. This is accomplished by anchoring the bottom edge of the specimen to a test base simulating intended end-use applications and applying a force parallel to the top of the specimen. The specimen is allowed to displace in its plane. Sheathing panels that are a component of a specimen shall be positioned such that they do not bear on the test frame during testing. (See Note 1.) As the specimen is racked to specified displacement increments, the racking (shear) load and displacements are continuously measured (see 8.7).
NOTE 1—If the end-use applications require sheathing panels bear directly on the sill plate, such as most structural insulated panels, the FIG. 1 Performance Parameters of Specimen: (A) Last Point atPu$0.8Ppeak
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FIG. 1 Performance Parameters of Specimen: (B) Last Point atPu= 0.8Ppeak(continued)
FIG. 2 Examples of Observed Hysteresis Curve and Envelope Curves for Test Method A
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specimen may be tested with sheathing panels that bear on the sill plate.
5. Significance and Use
5.1 These test methods are intended to measure the perfor- mance of vertical elements of the lateral force resisting system subjected to earthquake loads. Since these loads are cyclic, the loading process simulates the actions and their effects on the specimens.
6. Specimen
6.1 General—The typical specimen consists of a frame, bracing elements, such as panel sheathing, diagonal bracing, etc., and fastenings. The bracing is attached on one side of the frame unless the purpose of the test requires bracing on both sides. The elements of the specimen shall be fastened to the frame in a manner to conform to 6.2. Elements used to construct specimens may be varied to permit anticipated failure of selected elements. All detailing shall be clearly identified in the report in accordance with Section 10.
6.2 Connections—The performance of specimens is influ- enced by the type, spacing, and edge distance of fasteners attaching sheathing to framing and spacing of the shear connections and hold-down connectors, if applicable, and the tightness of the fasteners holding the specimen to the test base.
6.2.1 Sheathing Panel Attachments—All panel attachments shall be consistent with the types used in actual building construction. Structural details, such as fastener schedules,
fastener edge distance, and the gap between panels, shall be reported in accordance with Section 10.
6.2.2 Attachment to the Test Base—Specimen shall be attached to the test base with fasteners in a manner representing field conditions. For intended use requirements over a non- rigid foundation, a mock-up flexible base shall be constructed to simulate field conditions. Consideration shall be given to the orientation and type of floor joists relative to the orientation of the wall assembly. When strap connections are used, they shall be installed (that is, inside/outside the sheathing, etc.) without pre-tension in a configuration that simulates the field applica- tion. The test report shall include details regarding this attach- ment.
6.2.3 Anchor and Hold-Down Bolts—When the specimen frame is made of solid wood or wood-based composites, the anchor bolts shall be tightened to no more than finger tight plus a1⁄8turn, provided that the design value of stress perpendicular to the grain is not exceeded (seeNote 2). The hold-down bolts shall be tightened consistently between replicates in accor- dance with hold-down manufacturer’s recommendation. The assembly test shall not start within 10 min of the anchor bolt tightening to allow for stress relaxation of the anchor.
NOTE 2—Since solid wood and wood-based composites relax over time as well as potentially shrink due to changing moisture content, the intent of the finger tight plus a1⁄8turn is to avoid any significant pre-tension on the anchor bolts, which may affect the test results. It is the committee judgment that the maximum bolt tension should not be more than 300 lbf FIG. 2 Examples of Observed Hysteresis Curve and Envelope Curves for Test Method B(continued)
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(1.33 kN) for the purpose of ensuring the bolt is not caught on a thread or not seated fully. It should be noted that, however, the bolt tension depends on wood species and density, bolt thread pitch (or bolt diameter), and plate washer size. A general rule of thumb is to finger-tight plus1⁄8turn, which will result in a nut displacement of approximately 0.01 in. (0.254 mm) for
1⁄2and5⁄8-in.-diameter (12.7 and 15.9-mm-diameter) UNC bolts. A torque of about 50 lbf-in. (5.65 kN-mm) without bolt lubrication would normally produce 300 lbf (1.33 kN) of bolt tension.
6.3 Frame Requirements—The frame of the specimen shall consist of materials representative of those to be used in the actual building construction. The connections of these mem- bers shall be consistent with those intended in actual building construction.
6.3.1 For wood framing members, record the species and grade of lumber used (or the relevant product identification information for structural composite lumber framing); moisture content of the framing members at the time of the specimen fabrication and testing, if more than 24 h passes between these operations (see Test MethodsD4442, Test Methods A or B; or D4444, Test Methods A or B); and specific gravity of the framing members (see Test MethodsD2395, Test Method A).
The specific gravity of the framing members shall be repre- sentative of the published specific gravity for the product with no individual member exceeding the published value by more that 10 % (seeANSI/AF&PA NDSfor example).
6.3.2 For steel or other metal framing members, record the material specifications and thickness.
6.4 Structural Insulated Panel—The panel is prefabricated assembly consisting of an insulating core of 1.5 in. (38 mm) minimum sandwiched between two facings. The assembly is constructed by attaching panels together and to top and bottom plates or tracks.
6.5 Specimen Size—The specimen shall have a height and length or aspect (height/length) ratio that is consistent with intended use requirements in actual building construction (see Fig. 4).
7. Test Setup
7.1 The specimen shall be tested such that all elements and sheathing surfaces are observable. For specimens such as framed walls with sheathing on both faces of framing or frameless structural insulated panels, the specimens are dis- mantled after tests to permit observation of all elements.
7.2 The bottom of the specimen shall be attached to a test base as specified in 6.2. The test apparatus shall support the specimen as necessary to prevent displacement from the plane of the specimen, but in-plane displacement shall not be restricted.
7.3 Racking load shall be applied horizontally along the plane of the specimen using a double-acting hydraulic actuator with a load cell. The load shall be distributed along the top of the specimen by means of a loading beam or other adequate devices. The beam used to transfer loads between the hydraulic
FIG. 2 Examples of Observed Hysteresis Curve and Envelope Curves for Test Method C(continued)
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FIG. 3 Example of Average Envelope Curve (see Fig. 2, Test Method C)
FIG. 4 An Example of Shear Wall Specimen
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cylinder and the test specimen shall be selected so that it does not contribute to the measured racking strength and stiffness.
7.3.1 If applied to the top of the specimen directly, for example, as is shown inFig. 5, the maximum stiffness of load beam permitted is 330 000 kips-in.2(947 kN-m2) (seeNote 3).
NOTE 3—The selected stiffness corresponds with an HSS 53 3 3
1⁄4-in. (12737636.4-mm) steel section. Other sections with equal or less stiffness have been successfully employed.
7.3.2 The load beam selected shall not be continuous over discontinuities in the test specimen (seeNote 4).
NOTE 4—Examples of discontinuities include portal frame openings, wall perforations, transitions between differential bracing types, etc.
Continuation of a rigid load beam over these discontinuities can add to the measured in-plane rigidity of the system. However, the use of continuous load beam over discontinuities may be considered provided that the added in-plane rigidity can be justified by the end-use applications.
7.3.3 The combined gravity load applied to the specimen by the load beam and actuator shall be less than 350 lbf (1.56 kN), unless the purpose of the test includes the influence of vertical loads on the system performance (seeAppendix X3).
7.4 Test setup shall be designed and installed so that vertical (gravity) loads from test equipment applied to the specimen are negligible. Other vertical loads shall not be added to the
specimen unless justified by analysis of actual building con- struction or the objective of the testing. When vertical loads are applied, the magnitude and test setup for the vertical load shall be reported along with the justification.
NOTE 5—The neglect of vertical loads in this standard may result in inaccurate estimates of the capacity of the specimen as an element of the lateral force resisting system in actual building construction. For example, the neglect of uplift forces in testing may overestimate the racking capacity of the element, while the neglect of dead weight of the story above may underestimate the racking capacity of the element unless buckling is the predominant failure mode.
8. Procedure
8.1 Number of Tests—A minimum of two specimens of a given construction shall be tested if the shear strength (vpeak) values of each specimen calculated according to 9.1.1 are within 10 % of each other. The lower of the two test values shall be used to calculate the 10 % allowance. Otherwise, at least three specimens of a given construction shall be tested.
8.2 The cyclic displacement of the actuator shall be con- trolled to follow a cyclic displacement procedure described in either 8.3(Test Method A),8.4(Test Method B), or8.5(Test Method C).
FIG. 5 An Example of Test Setup for Shear Wall Specimen
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8.3 Test Method A (Sequential-Phased Displacement Proce- dure):
8.3.1 Sequential Phased Displacement (SPD) Loading Protocol—Displacement-controlled loading procedure that in- volves displacement cycles grouped in phases at incrementally increasing displacement levels. The cycles shall form either a sinusoidal wave or a triangular wave. The SPD loading consists of two displacement patterns and is illustrated inFig.
6. The first displacement pattern consists of three phases, each containing three fully-reversing cycles of equal amplitude, at displacements representing 25 %, 50 %, and 75 % of antici- pated FME. The second displacement pattern is illustrated in Fig. 7. Each phase is associated with a respective displacement level and contains one initial cycle, three decay cycles, and a number of stabilization cycles. For nailed wood-frame walls, three stabilization cycles are sufficient to obtain a stabilized response. The amplitude of each consecutive decay cycle decreases by 25 % of the initial displacement.
8.3.2 The schedule of amplitude increments between the sequential phases is given in Table 1. The amplitude incre- ments selected for the SPD procedure are based on the FME determined from the static monotonic load test on an identical specimen in accordance with Practice E564. To determine Dyield, it is permitted to compute EEEP curves, as shown inFig.
1 based on monotonic test data, in accordance with9.1.4.
8.4 Test Method B (ISO 16670 Protocol):
8.4.1 ISO Displacement Schedule—Displacement- controlled loading procedure that involves displacement cycles grouped in phases at incrementally increasing displacement levels. The ISO loading schedule consists of two displacement patterns and is illustrated in Fig. 8. The first displacement pattern consists of five single fully reversed cycles at displace- ments of 1.25 %, 2.5 %, 5 %, 7.5 %, and 10 % of the ultimate
displacementDm. The second displacement pattern consists of phases, each containing three fully reversed cycles of equal amplitude, at displacements of 20 %, 40 %, 60 %, 80 %, 100 %, and 120 % of the ultimate displacement Dm.
8.4.2 The sequence of amplitudes, which is given inTable 2, are a function of the mean value (where applicable) of the ultimate displacement (Dm) obtained from matched specimens in the monotonic tests in accordance with Practice E564.
8.5 Test Method C (CUREE Basic Loading Protocol):
8.5.1 CUREE Basic Loading Protocol—Displacement- controlled loading procedure that involves displacement cycles grouped in phases at incrementally increasing displacement levels. The loading history starts with a series of (six) initiation cycles at small amplitudes (of equal amplitude). Further, each phase of the loading history consists of a primary cycle with amplitude expressed as a fraction (percent) of the reference deformation,D, and subsequent trailing cycles with amplitude of 75 % of the primary one.
NOTE 6—The initiation cycles serve to check loading equipment, measurement devices, and the force-deformation response at small am- plitudes.
8.5.2 The schedule of amplitude increments is given in Table 3and is illustrated inFig. 9. The reference deformation Dshall be an estimate of the maximum displacement at which the load in a primary cycle has not yet dropped below 0.8Ppeak. The value ofDshall not exceed 0.025 times the wall height. If the panel has not failed at the end of Phase 8 ofTable 3, then additional phases shall be added. Each subsequent phase shall consist of a primary cycle with an increase in amplitude ofa (a # 0.5) over the previous primary cycle, and followed by two trailing cycles with amplitude of 75 % of the primary one.
FIG. 6 Cyclic Displacement Schedule (Test Method A)
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8.6 The actuator displacement in Test Methods A, B, or C shall be controlled at either constant cyclic frequency or at a constant rate of displacement. The rate of displacement shall be between 0.04 and 2.5 in./s (1.0 and 63.5 mm/s). The cyclic frequency shall range from 0.2 to 0.5 Hz to avoid inertial
effects of the mass of the wall and test fixture hardware during cyclic loading. The loading shall follow the corresponding procedure until the applied load diminishes more than 0.2 Ppeak, that is, until the failure limit state occurs.
FIG. 7 Single Phase of Pattern 2 (Test Method A)
FIG. 8 Cyclic Displacement Schedule (Test Method B)
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8.7 Displacements shall be measured with displacement measuring devices with a resolution of 0.005 in. (0.13 mm) or
other suitable devices for continuously measuring displace- ment under cyclic loading conditions, at a minimum sampling
FIG. 9 Cyclic Displacement Pattern (Test Method C)
TABLE 1 Test Method A—Amplitudes of Initial Cycles Pattern Step Minimum Number
of CyclesA
Amplitude of Initial Cycle
% FME
1 1 3 25
2 3 50
3 3 75
2 4 7 100
5 7 125
6 7 150
7 7 175
8 7 200
9 7 250
10 7 300
11 7 350
12 Additional increments of
50 (until specimen failure)
ASee8.3.1for details.
TABLE 2 Test Method B—Amplitudes of the Reversed Cycles Pattern Step Minimum Number
of Cycles Amplitude, %Dm
1 1 1 1.25
2 1 2.5
3 1 5
4 1 7.5
5 1 10
2 6 3 20
7 3 40
8 3 60
9 3 80
10 3 100
11 3 Additional increments of
20 (until specimen failure)
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rate of 100 readings per cycle. The following instrumentation shall be provided for measuring displacements, and hold-down connector forces when required:
8.7.1 Horizontal displacement of the specimen at the top plate.
8.7.2 Vertical (upward and downward) displacement of both end posts (or equivalent) relative to the rigid base. The reference point for this measurement shall be on or immedi- ately adjacent to the outside face of the end post.
8.7.3 Horizontal displacement of the bottom plate relative to the rigid base (lateral in-plane sliding).
8.7.4 Vertical displacement of the hold-down connectors relative to the end posts (deformation of the connectors and fastener slip), as applicable.
8.7.5 When specified, loads on the bolts fastening the hold-down connectors to the rigid base.
9. Calculation
9.1 Based on the observed hysteresis response curves, the envelope (positive and negative) curves are generated for each tested specimen. If the laboratory chooses to report the positive and negative performances individually, then both envelopes (positive and negative) shall be analyzed separately in accor- dance with Section9. If the laboratory chooses to report one set of performance parameters that characterizes both envelopes, then the positive and negative envelope curves shall be averaged to produce an average envelope curve according to 3.2.4 and the calculations outlined in Section 9 shall be conducted for each specimen based up the average envelope curve.
NOTE 7—If the specimen behavior in the positive and negative quad- rants is similar (major events occur in the same phases on the negative and positive sides), a reasonable approximation of the average performance can be achieved by determining the parameters from positive and negative envelopes individually and then averaging them (seeAppendix X4).
9.1.1 Shear Strength (npeak) lbf/ft (N/m)—The maximum load per unit specimen length resisted by the specimen in the given envelope shall be calculated as follows:
npeak 5Ppeak
L (1)
where:
Ppeak = maximum load resisted by the specimen in the given envelope, lbf (N); and
L = length of specimen, ft (m).
9.1.2 Secant shear modulus, G8, at 0.4 Ppeak and at Ppeak shall be calculated as follows:
G85P D3H
L (2)
where:
G8 = shear modulus of the specimen obtained from test (includes shear and uplift deformation for the connec- tion system), lbf/in. (N/m); represents the secant shear stiffness at specified specimen displacements times the aspect ratio;
P = applied load measured at the top edge of the speci- men, lbf (N);
D = displacement of the top edge of the specimen based on test, in. (m). This includes both the shear deflection of the sheathing material and its connections, and the contribution of the shear and hold-down connection systems;
H = height of specimen, ft (m); and L = length of specimen, ft (m).
9.1.3 Cyclic ductility ratio,D, as described in3.2.1, shall be calculated. If the shear stiffness (shear modulus) at 0.4Ppeakis greater than that atPpeak, generate the EEEP curve as described in 9.1.4. Otherwise, the FME and the ultimate displacement shall be determined directly from the envelope curve. Calculate values of displacement, shear forces, and shear modulus at the yield limit state and strength limit state.
9.1.4 When specified by9.1.3, develop an EEEP curve to represent the envelope curve. Fig. 1 illustrates typical EEEP curve. The elastic portion of the EEEP curve contains the origin and has a slope equal to the elastic shear stiffness, Ke. The plastic portion is a horizontal line equal to Pyield deter- mined by the following equation:
Pyield5
S
Du2Œ
Du222AKeD
Ke (3)IfDu2,2A
Ke, it is permitted to assumePyield50.85Ppeak where:
Pyield = yield load, lbf (N);
A = the area under envelope curve from zero to ulti- mate displacement (Du) of the specimen, lbf·in.
(N·m);
TABLE 3 Test Method C—Amplitude of Primary Cycles Pattern Step Minimum Number
of Cycles
Amplitude of Primary Cycle, %D
1 1 6 5
2 2 7 7.5
3 7 10
3 4 4 20
5 4 30
4 6 3 40
7 3 70
8 3 100
9 3 100 + 100aA
10 3 Additional increments of
100a(until specimen failure)
Aa#0.5.
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Ppeak = maximum absolute load resisted by the specimen in the given envelope, lbf (N);
De = displacement of the top edge of the specimen at 0.4Ppeak, in. (mm); and
Ke = 0.4Ppeak/De.
9.1.4.1 To generate an EEEP curve as described in 8.3.2 based on monotonic test results, the procedures in this section are permitted, withDmsubstituting for Du.
9.1.5 If the envelope curve contains data points at loads less than |0.8Ppeak| (past strength limit state), the failure limit state shall be determined at 0.8Ppeakusing linear interpolation, as illustrated in Fig. 1.
10. Report
10.1 The report shall include the following information:
10.1.1 Date of the test and of report.
10.1.2 Names of the test sponsors and test agency and their locations.
10.1.3 Identification of the specimen (test number, and so forth).
10.1.4 Detailed description of the specimen and the test setup, including the following:
10.1.4.1 Dimensions of the specimen.
10.1.4.2 Details of the physical characteristics or structural design, or both, of the specimen, including, if applicable, the type, spacing, and edge distance of fasteners attaching sheath- ing to framing.
10.1.4.3 Details of attachment of the specimen in the test fixture, including a description of the test base and whether sheathing panels are directly bearing on the sill plate during testing.
10.1.4.4 Location of load application and load cell, strain gauges, deflection gauges, and other items for test as appli- cable.
10.1.4.5 Description of construction materials (for example, material type and grade, thickness, yield point, tensile strength, compressive strength, density, moisture content, manufacturer of components used, source of supply, dimensions, model, type, and other pertinent information, and so forth, as appro- priate for materials used).
10.1.4.6 Drawing showing plan, elevation, principal cross section, and other details as needed for description of the specimen and the test setup (see10.1.4.1-10.1.4.5).
10.1.4.7 Description of general ambient conditions includ- ing the following:
(1)At construction;
(2) During curing or seasoning, if applicable (including elapsed time from construction to test); and
(3)At test.
10.1.4.8 Modifications made on the specimen during test- ing.
10.1.4.9 Description of any noted defects existing in the specimen prior to test.
10.1.5 Description of the test, including a statement that the test or tests were conducted in accordance with this test method or otherwise describing any deviations from the test method.
10.1.6 Summary of results, including:
10.1.6.1 Hysteresis loops (applied load versus displacement at the top of the specimen) for every specimen tested.
10.1.6.2 Complete record (table or plot) of individual dis- placements required to be measured in8.7.
10.1.6.3 Shear strength (npeak) from tests of identical speci- mens (9.1.1).
10.1.6.4 As-tested and mean values ofP,DandG8at yield limit state and strength limit state in accordance with Section9.
10.1.6.5 EEEP curve developed from the mean loads and displacements at yield limit state and failure limit state, if applicable (see9.1.3and9.1.4).
10.1.7 Description of failure modes and any behavior change and significant events, for each test.
10.1.8 Photographs of the specimen, particularly those de- picting conditions that cannot otherwise be easily described in the report text, such as failure modes and crack patterns.
10.1.9 Appendix (if needed) that includes all data not specifically required by test results. Include special observa- tions for building code approvals.
10.1.10 Signatures of responsible persons are in accordance with PracticeE575.
11. Precision and Bias
11.1 No statement on the precision and bias is offered due to the numerous individual elements that comprise the specimen and the small number of replicate specimens tested. A gener- ally accepted method for determining precision and bias is currently unavailable.
12. Keywords
12.1 cyclic loads; earthquake; framed walls; lateral-force resisting systems; portal frames; racking loads; rigid support;
shear displacement; shear stiffness; shear strength; structural insulated panels
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APPENDIXES
(Nonmandatory Information)
X1. DETERMINATION OF FIRST MAJOR EVENT X1.1 The FME is the first significant limit state that occurs
during the test. The limit state in turn denotes an event marking phase change between two behavior states. As noted in8.3.2, the FME can be determined from monotonic load tests on an identical specimen. If the first estimate is inappropriate, the data obtained can be revised for the subsequent tests. The following estimates offer guidance for a typical 8-ft (2.4-mm) wall.
X1.1.1 Wood-Framed Walls with Wood Structural Panel Sheathing—Aspect ratios of 2:1 or less, FME = 0.8 in. (20 mm); aspect ratio of 4:1, FME = 1.2 in. (31 mm).
X1.1.2 Wood-Framed Walls with Gypsum Sheathing—
Aspect ratios of 2:1 or less, FME = 0.25 in. (6.4 mm).
X2. SELECTION OF CYCLING METHOD X2.1 Test Method A Versus Test Method B
X2.1.1 Test Method A:
X2.1.1.1 Test Method A is a sequential phased displacement pattern that exhibits decay cycles between the steps in the loading pattern. These decay cycles provide information on whether there is a lower bound in displacement required to produce hysteretic energy dissipation(1).5An example where a lower bound displacement causing hysteretic energy dissipa- tion may occur would be a bolted connection through an over-drilled hole.
X2.1.1.2 Test Method A is based on Ref (2), which was developed by the Structural Engineers Association of Southern California (SEAOSC) to test wood or steel framed shear walls for earthquake resistance. The Ref (2) is currently not being maintained. There is a considerable breadth of information and vast databases on walls tested under Ref(2). For the purposes of acceptance testing it would be permissible to correlate the results of the two test methods.
X2.1.2 Test Method B:
X2.1.2.1 The cyclic protocol for Test Method B was devel- oped for ISO 16670, a method for testing mechanically fas- tened timber joints. The background for this standard is given in Ref(3-6), which indicates that a unique cyclic displacement or loading history will always be a compromise, but one that is conservative for most practical cases should be selected. The Test Method B test protocol is intended to produce data that sufficiently describe elastic and inelastic cyclic properties; and typical failure mode that is expected in earthquake loading.
X2.1.3 Selection of Test Method A Versus Test Method B:
X2.1.3.1 Test Method A may be applicable to systems when FME is the yield limit state or for testing slack systems to determine a lower bound displacement causing hysteretic energy dissipation. Test Method B is a ramped displacement phase that bases the cycles on the percentage of an ultimate displacement determined through static tests. Test Method B may be more applicable to systems that exhibit linear elastic
behavior where FME is the strength limit state. If the ratio of Dm and FME is less than three, Test Method B may be preferable. Both test methods are intended to generate similar displacement amplitudes in order to obtain similar number of points in the envelope curves. The difference is the number of cycles in each phase (step).
X2.2 Test Method C
X2.2.1 Test Method C (CUREE protocol) is the latest addition to the family of cyclic test protocols. It was developed based on the statistical analysis of seismic demands on light-frame buildings representative of California (in particular Los Angeles) conditions. The CUREE basic loading history is a realistic and conservative representation of the cyclic defor- mation history to which a component of a wood structure likely is subjected in earthquakes(7,8). At relatively large deforma- tions (primary cycles exceeding an amplitude of 0.4 D), the amplitude of the primary cycles increases by large steps. These large steps are based on statistics of inelastic time history responses. If the purpose of the experiment is acceptance testing, then it is permissible to reduce the step size of the primary cycles with large amplitudes. Smaller step sizes close to failure may result in a larger capacity (largest amplitude at which the acceptance criteria are met), even though they will result in larger cumulative damage. The reason is that the large step sizes of the basic loading history permit evaluation of acceptance only at discrete and large amplitude intervals. This standard permits a reduction in step size only for phases in which the amplitude of the primary cycle exceeds D. In that regime the amplitude the primary cycle may be increased by aD, withato be chosen by the user, buta#0.5.
X2.2.2 The reference deformation, D, is a measure of the deformation capacity (Du) of the specimen when subjected to the cyclic loading history. It is used to control the loading history, and therefore needs to be estimated prior to the test.
The estimate can be based on previous experience, the results of a monotonic test, or a consensus value that may prove to be useful for comparing tests of different details or configurations.
In CUREE Project(7), the following guidelines were used:
5The boldface numbers in parentheses refer to a list of references at the end of this standard.
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X2.2.2.1 Perform a monotonic test, which provides data on the monotonic deformation capacity, Dm. This capacity is defined as the deformation at which the applied load drops, for the first time, below 80 % of the maximum load that was applied to the specimen.
X2.2.2.2 Use a specific fraction ofDm, that is,gDm, as the reference deformation for the basic cyclic load test. At this
time, a value ofD= 0.6Dmis suggested. The factorgshould account for the difference in deformation capacity between monotonic test and a cyclic test in which cumulative damage will lead to earlier deterioration in strength.
X3. TEST SETUP
X3.1 CUREE recommendations(9)suggest that top of wall boundary conditions may influence wall test results. The weight of the load beam and actuator on a test specimen can reduce the anchorage demand in a specimen tested in a vertical orientation. The inertia from a heavy load beam during a cyclic test will exaggerate the measured response in test frames that test a wall either vertically or horizontally. For these reasons, the mass of the load beam and any hydraulics supported by the specimen shall be minimized to the extent practical. In test
setups where vertical load from the actuator is carried by the test setup, the impact of the actuator mass may be evidenced by the difference in the positive and negative response from a symmetrical system. Test frames have been constructed that do not impose any vertical load on the specimen. The 350-lbf (1.56-kN) load limit is based on committee judgment that considered a range of test frames that are successfully employed.
X4. COMMENTARY X4.1 Performance Parameters—It is always permissible to
analyze the positive and negative envelope curves for a specimen individually and report the corresponding response parameters without averaging. However, the method for com- puting average performance parameters that characterize both envelopes (positive and negative) can make a difference when a specimen shows an asymmetrical response. In laboratory practices, the responses from most wall tests are asymmetrical to some degree as damage created with an initial positive excursion tends to weaken the response from the subsequent negative excursion within the same cycle. Determining the average response parameters for a specimen with dissimilar positive and negative envelope curves by analyzing each envelope (positive and negative) individually and then averag- ing can result in non-conservative estimates of the perfor- mance. Therefore, it is the committee judgment that when one set of parameters is used to summarize the specimen response for structural design purposes, the parameters should be calculated from the average envelope as the primary method of analysis. Using this approach reduces the non-conservatism for
a moderately asymmetric wall. Calculation of average param- eters individually from the negative and the positive envelopes will provide a practical approximation of the average param- eters for reasonably symmetric envelopes; that is, if major events occur in the same phases on the negative and the positive sides. Caution and judgment should be used in estimating any form of average response to characterize a system that is grossly asymmetric. In these instances, the positive and negative envelopes should always be analyzed and reported individually without averaging.
X4.2 Number of Tests—Depending on the purpose of a testing program, the minimum number of tests required in8.1 may require an adjustment. For example, if the test program is intended for an exploratory study, the number of tests (two) specified in8.1may be sufficient. On the other hand, if the test program is intended for code acceptance, three to five replica- tions are typically required by the code evaluation agencies for a specific specimen configuration.
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REFERENCES
(1)Porter, M. L., “Sequential Phased Displacement (SPD) Procedure for TCCMAR Testing,” Proceedings of Third Meeting of the Joint Technical Coordinating Committee on Masonry Research, U.S./Japan Coordinated Earthquake Research Program, Tomamu, Japan, 1987.
(2)Structural Engineers Association of Southern California, Standard Method of Cyclic Reverse Load Tests for Shear Resistance of Framed Walls for Buildings,Sacramento, CA, 1997.
(3)Park, R., “Evaluation of Ductility of Structural & Structural Assem- blages from Laboratory Testing,” Bulletin of the New Zealand Society for Earthquake Engineering, Vol 22, No. 3, September 1989.
(4) Chopra, A. K., Dynamics of Structures—Theory and Applications to Earthquake Engineering,” Prentice-Hall, Inc., Englewood Cliffs, NJ, 1995.
(5) Foliente, G. C., Karacabeyli, E., and Yasumura, M., “International Test Standards for Joints in Timber Structures under Earthquake and Wind Loads,” Proceedings of Structural Engineering World Congress, Ref
T222-6, San Francisco, CA, 1998.
(6) Foliente, G. C., and Zacher, E. G., “Performance Tests of Timber Structural Systems Under Seismic Loads. Analysis, Design, and Testing of Timber Structures Under Seismic Loads,” Proceedings of Research Needs Workshop, available from University of Californi- a–Berkeley, Forest Products Laboratory, Richmond, CA, 1994.
(7)Krawinkler, H., Parisi, F., Ibarra, L., Ayoub, A., and Medina, R.,
“Development of a Testing Protocol for Wood Frame Structures,”
CUREE Publication No. W-02, 2000.
(8)White, M. W., and Dolan, J. D., “Nonlinear Shear-Wall Analysis,”
ASCE Journal of Structural Engineering, American Society of Civil Engineers, New York, NY, November 1995.
(9)Cobeen, K, Russell, J., and Dolan, J. D., “Recommendations For Earthquake Resistance in the Design and Construction of Woodframe Buildings,” CUREE Publication No. W-30, 2003.
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